OBJECTIVE Application of spatially filtered magnetoencephalography (MEG) to investigate changes in the mechanism of cerebral motor control in patients with tumours around the central sulcus. METHODS MEG records were made during a repetitive hand grasping task in six patients with gliomas around the central sulcus and in four control subjects. Power decreases in the alpha (8-13 Hz), beta (13-30 Hz), and low gamma bands (30-50 Hz) during the motor tasks (event related desynchronisation, ERD) were analysed statistically with synthetic aperture magnetometry. The tomography of ERD was superimposed on the individual's magnetic resonance image. RESULTS beta ERD was consistently localised to the contralateral primary sensorimotor cortex (MI/SI) in control subjects, whereas the alpha and low gamma ERD showed considerable intersubject variability. beta ERD in patients during non-affected side hand movement was also localised to the contralateral MI/SI, but exclusively to the ipsilateral hemisphere during affected side hand movement. CONCLUSIONS The altered pattern of ERD in the patient group during affected side hand movement suggests recruitment of diverse motor areas, especially the ipsilateral MI/SI, which may be required for the effective movement of the affected hand.